The invention relates to a flow duct particularly an intake duct, in an intake system and a cylinder head of an internal-combustion engine, in which a gas flow is controlled by means of a valve which comprises a valve disk interacting with a valve seat and a valve stem which is connected with it and, in an axially movable manner, is disposed in a valve stem guide, the valve stem being arranged adjacent to the valve seat ring in the intake duct in such a manner that it is subjected to the gas flow.
In a known flow duct, described in German Patent Document DE-OS 35 08 763, the flow profile is designed such that it tapers continuously in the direction of the valve seat ring. This design is a result of the physical principle that the lowest losses, when the flow is unimpaired, occur in a flow duct if the cross section of the flow duct narrows down continuously and the velocity of the gas flow is increased continuously. However, in the case of a flow duct having a valve, an unimpaired flow cannot always be implemented because this valve causes a considerable flow resistance which, together with a flow profile of this type, impairs an optimized operation of an internal-combustion engine.
It is an object of the invention to construct an intake duct for an internal-combustion engine in such a manner that the flow rate of the gas flow takes into account the resistance caused by the inlet valve with the aim toward better operating characteristics of the internal-combustion engine.
This object is achieved by means of an arrangement wherein the intake duct is divided into a first duct section in the intake system and a second duct section of the cylinder head disposed downstream of the first duct section, said intake duct being provided with a defined flow profile which, until it reaches a cross-sectional transition are situated relatively close in front of the valve stem, has a uniform cross-sectional contraction and, behind it, has a uniform cross-sectional widening.
The principal advantages achieved by means of the invention are that the gas flow in the two duct sections of the suction pipe system and the cylinder head has an optimized flow rate course, whereby the gas flow is accelerated to the cross-sectional transition area and is decelerated behind it. The latter causes a reduction of the flow resistance, whereby the degree of delivery of the internal combustion engine is improved. This, in turn, increases the output and reduces the consumption.
Reference is also made to related, commonly assigned U.S. patent application Ser. No. 07/554,895, filed July 20, 1990, based on German patent application P 39 24 543.8 filed in Germany on July 25, 1989.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.